1. Field of the Invention
The invention relates to a dual-speed single-phase AC motor.
2. Description of the Related Art
Nowadays, single-phase AC motors are widely used, among which approximately 20% operate at rated speed, and above 80% operate after varying speed. Most single-phase AC motors adjust speed by reducing voltage, for example, by tap of winding, connection of reactance and so on. Relationship between voltage and power is P=U2/R, R is a constant, and the power is proportional to the square of voltage. All these methods implement adjustment of speed by reducing input voltage. As a range of adjusting speed is comparatively wide, adjustment of output power is difficult to be implemented. In other words, adjustment of speed via variation of output power features comparatively narrow adjustment range, which makes it difficult to meet requirement for loads, and for various application of uses.
Although pole-changing adjustable-speed single-phase AC motors appear recently, they use mechanical centrifugal switches to implement switching and control functions, the mechanical centrifugal switches are opened under the action of centrifugal force, and switch off starting circuits and operate. During on/off of the mechanical centrifugal switches, electric arc spark is generated, which reduces work life thereof. Moreover, starting circuits thereof feature poor controllability and low control accuracy, and motors using the same have low operation reliability.